The present invention relates to a polyurethane geotextile composite having improved water resistance. Additionally, the present invention relates to a process for forming a polyurethane geotextile composite having improved water resistance.
In recent years, the management of natural resources has become important in many countries throughout the world. Efforts have been directed both toward the conservation of our resources and toward the elimination of pollution from our environment. Particular emphasis has been placed on waste leakage and water loss.
Losses in the distribution of water using unlined irrigation ditches are estimated at a minimum to be 25% and in some situations to be more than 50% depending upon the porosity of the ditch surface and the distance the water is being moved. In most rural areas, ditches are formed by excavating the soil to the desired depth and width. The water moves through the ditch in contact with the exposed natural surface. This can be sand, clay, rocks, etc. and, more commonly, mixtures thereof. The porosity will depend upon the proportions of the different components in the soil.
The loss of water in unlined irrigation ditches at one time was considered acceptable only because the supply of water exceeded demand. However, as civilization has developed and world population has increased, more water is required for both greater food production and for the marked by increasing in non-agriculture uses. In addition to greater domestic uses in sanitation, industry now employs large quantities of water in manufacturing and processing procedures.
This high level of consumption plus the very high cost of developing new water supplies has shifted attention to water conservation. Domestic appliances that use less water have been developed. Also, industry has installed recycling purification systems to reduce water consumption.
Although conservation efforts have reduced water consumption to a degree, water is still in relatively short supply, particularly in recent years with the severe droughts in the United States and other countries. Since the most cost effective conservation opportunities and readily accessible water supplies already have been developed, greater attention must be directed to improving the efficiency of water distribution systems.
Improvements in water distribution have been made. A limited number of ditches and canals have been lined with concrete and/or preformed concrete pipes. Concrete is durable and has a long life when properly used. However, concrete is expensive to place and finish and is damaged by unfavorable temperatures during curing. Also, concrete is subject to frost damage, cracking and heaving which results in leaks.
Processes for forming composite liners for canals and ditches and apparatus to perform such a processes are disclosed, for example, in U.S. Pat. Nos. 4,872,784; 4,955,759; 4,955,760; 5,049,006; 5,062,740; and 5,421,677.
However, the above-noted patents give almost no guidelines as to the solidifiable compositions which should be used. For example, U.S. Pat. No. 4,872,784 (at column 5, lines 55-60), U.S. Pat. No. 4,955,759 (at column 5, lines 58-63), U.S. Pat. No. 4,955,760 (at column 4, lines 55-60) and U.S. Pat. No. 5,062,740 (at column 4, lines 56-61) broadly suggest the use of a foamed polyurethane resin but no specific formulations are taught or suggested. U.S. Pat. No. 5,049,006 (at column 4, lines 26-32) and U.S. Pat. No. 5,145,282 (at column 5, line 64xe2x80x94column 6, line 2) broadly suggest the use of a thermosetting resin forming mixture such as a polyester or a polyurethane forming mixture, without describing any specific formulations.
U.S. Pat. No. 5,421,677 (xe2x80x9cthe ""677 patentxe2x80x9d) is directed to an improved process for forming a ditch liner. The ""677 patent discloses the use of a mixture of one or more polyisocyanates, a polyol mixture, one or more fillers, and a catalyst. The mixture of the ""677 patent is dispensed on a geotextile, thereby forming a liquid polyurethane soaked geotextile composite. The liquid polyurethane soaked geotextile composite is then placed over the surface of an area to be lined and allowed to cure, to form a polyurethane/geotextile composite. One drawback of the mixture taught by the ""677 patent is that the filler in the mixture is often not completely dry and can absorb additional moisture from the atmosphere. Moisture is always present when the mixture is applied under relatively humid conditions. This water will react with the polyisocyanate and cause the mixture to foam. Foaming weakens the strength and impermeability of the composite.
Even when completely dry fillers are used in the mixture under non-humid conditions, the polyurethane geotextile composite, when stored under water (such as in a ditch or canal liner application), can absorb considerable amounts of water (i.e., 1-2%) which swells and weakens the liner.
For the foregoing reasons, it would be desirable to develop an improved polyurethane composition that does not foam, even when applied under humid conditions and is less sensitive when wet filler is used in the polyurethane composition. Additionally, it would be desirable to develop a polyurethane geotextile composite liner that has substantially lower water absorption.
The present invention relates to a polyurethane geotextile composite with improved water resistance useful as a liner for a ditch or canal in which the polyurethane used is a reaction product of a mixture comprising:
a) a liquid polyisocyanate having an isocyanate content of at least 10% by weight,
b) an isocyanate-reactive component comprising:
(i) 20 to 90% by weight, based on total weight of b), of castor oil having an OH number of from about 160 to about 170, a viscosity of from about 500 to about 900 mPaxc2x7s at 25xc2x0 C., and a water content of less than 0.5% by weight, based on the total weight of castor oil;
(ii) 10 to 80% by weight, based on total weight of b), of a polyether polyol having an OH number of from 28 to 700, a functionality of from 2 to 8, a number average molecular weight of from about 240 to about 6,000, and a viscosity of from 50 to 35,000 mPaxc2x7s at 25xc2x0 C., in which at least 70% by weight of the alkylene oxide content is propylene oxide; and
(iii) from 0 to 10% by weight, based on total weight of component b), of a low molecular weight diol or triol having an equivalent weight of 31 to 99; and
c) a catalyst for the reaction of hydroxyl groups with isocyanate groups; and optionally,
d) a filler.
The invention further relates to a process for producing a polyurethane geotextile composite liner with improved water resistance in which a geotextile is impregnated with such polyurethane.
The invention is also directed to a ditch or canal lined with such polyurethane geotextile composite and to a process for lining a ditch or canal with such composite.
The advantage of the polyurethane composition used to produce the composite of the present invention is that it has less tendency to foam. The geotextile polyurethane composite of the present invention will, therefore, be characterized by low water absorption. When such composite is used to line a ditch and/or a canal, water loss is kept at a minimum.
The present invention relates to a polyurethane geotextile composite which is suitable for use as a liner with improved water resistance which is produced by impregnating a geotextile with a polyurethane composition that is a reaction product of a mixture which includes:
a) a liquid polyisocyanate having an isocyanate content of at least 10% by weight,
b) an isocyanate-reactive component which includes:
(i) from 20 to 90% by weight, based on total weight of b), of castor oil having an OH number of from about 160 to about 170, a viscosity of from about 500 to about 900 mPaxc2x7s at 25xc2x0 C., and a water content of less than 0.5% by weight, based on the total weight of castor oil;
(ii) from 10 to 80% by weight, based on total weight of b), of a polyether polyol having an OH number of from 28 to 700, a functionality of from 2 to 8, a number average molecular weight of from about 240 to about 6,000, and a viscosity of from 50 to 35,000 mPaxc2x7s at 25xc2x0 C., the polyether polyol being prepared by reacting initiator with one or more alkylene oxides in which at least 70% by weight of the total alkylene oxide is propylene oxide; and
(iii) from 0 to 10% by weight, based on total weight of component b) of a low molecular weight (i.e., molecular weight less than 240 (number average)) diol or triol having an equivalent weight of from 31 to 99,
c) a catalyst which catalyzes the reaction between hydroxyl groups and isocyanate groups; and optionally,
d) a filler.
The invention is also directed to a method for making such composites, ditches and canals lined with such composites and to a method for lining ditches and canals with such composites. A ditch or canal is lined with the polyurethane geotextile composite of the present invention by dispensing a polyurethane composition having improved water resistance onto a geotextile or otherwise impregnating the geotextile with the polyurethane composition, laying the polyurethane-impregnated geotextile onto a surface of a ditch or canal before the polyurethane has fully cured, conforming the polyurethane impregnated geotextile to the shape of the surface of the ditch or canal, and allowing the polyurethane to fully cure to form a polyurethane geotextile composite liner. The polyurethane composition having improved water resistance is a reaction product of the above described components a), b) and c).
The polyurethane composition having improved water resistance may be applied onto one or more geotextiles. A second polyurethane impregnated geotextile may be laid on the surface of a canal or ditch which has previously been lined with the liquid polyurethane composition is fully cured, if desired. Subsequently the polyurethane-impregnated geotextile is conformed to the shape of the surface of the canal or ditch where the polyurethane geotextile composite is allowed to fully cure. The polyurethane composition having improved water resistance used in this process is less likely to foam under humid conditions and produces a composite with less water absorption.
As used herein, the term xe2x80x9cgeotextilexe2x80x9d refers to any woven or non-woven porous blanket or mat which is produced from natural or synthetic fibers. Also, as used herein, the terms xe2x80x9cditchxe2x80x9d and xe2x80x9ccanalxe2x80x9d are used interchangeably and can refer to any liquid carrying surface having a depression or grade.
Geotextiles are used primarily to line earthen surfaces. Such liners may, however, also be used to line roofs, ponds, reservoirs, landfills, underground storage tanks, canals and ditches. Examples of geotextiles include woven or non-woven polypropylene, polyester, jute, cotton and fiberglass fabrics. Any of the known goetextiles may be used in the practice of the present invention.
Any of the known liquid isocyanates having an isocyanate content of at least 10% by weight, preferably at least 20% by weight, most preferably at least 30% by weight, which are liquid under the processing conditions used may be used in the practice of the present invention. Suitable liquid organic polyisocyanates include aliphatic, cycloaliphatic, araliphatic, aromatic, and heterocyclic polyisocyanates of the type described, for example, by W. Siefken in Justus Liebigs Annalen der Chemie, 562, pages 75 to 136. Such isocyanates include those represented by the formula Q(NCO)n in which n represents a number from 2 to about 5, preferably 2 to 3, and Q represents an aliphatic hydrocarbon group containing from 2 to about 18, preferably 6 to 10, carbon atoms, a cycloaliphatic hydrocarbon group containing from 4 to about 15, preferably from 5 to 10, carbon atoms, an araliphatic hydrocarbon group containing from 8 to 15, preferably from 8 to 13, carbon atoms, or an aromatic hydrocarbon group containing from 6 to about 15, preferably 6 to 13, carbon atoms. Examples of suitable isocyanates include: ethylene diisocyanate; 1,4-tetramethylene diisocyanate; 1,6-hexamethylene diisocyanate; 1,12-dodecane diisocyanate; cyclobutane-1,3-diisocyanate; cyclohexane-1,3- and 1,4-diisocyanate, and mixtures of these isomers; 1-isocyanato-3,3,5-trimethyl-isocyanatomethylcyclohexane (xe2x80x9cisophorone diisocyanatexe2x80x9d (See, e.g. German Offenlegungsschrift 1,202,785 and U.S. Pat. No. 3,401,190)); 2,4- and 2,6-hexahydrotoluene diisocyanate and mixtures of these isomers; dicyclohexylmethane-4,4xe2x80x2-diisocyanate (xe2x80x9chydrogenated MDIxe2x80x9d, or xe2x80x9cHMDIxe2x80x9d); 2,4- and 2,6-toluene diisocyanate and mixtures of these isomers (xe2x80x9cTDIxe2x80x9d); diphenylmethane-2,4xe2x80x2- and/or -4,4xe2x80x2-diisocyanate (xe2x80x9cMDIxe2x80x9d); polymethylene poly(phenylisocyanates) of the kind which may be obtained by condensing aniline with formaldehyde, followed by phosgenation (xe2x80x9ccrude MDIxe2x80x9d) (which are described, for example, in British Patents 878,430 and 848,671); norbornane diisocyanates (such as those described in U.S. Pat. No. 3,492,330); m- and p-isocyanatophenyl sulfonylisocyanates (of the type described in U.S. Pat. No. 3,454,606); perchlorinated aryl polyisocyanates (of the type described, for example, in U.S. Pat. No. 3,227,138); modified polyisocyanates containing carbodiimide groups (of the type described in U.S. Pat. No. 3,152,162); modified polyisocyanates containing urethane groups (of the type described, for example, in U.S. Pat. Nos. 3,394,164 and 3,644,457); modified polyisocyanates containing allophanate groups (of the type described, for example, in British Patent 994,890, Belgian Patent 761,616, and published Dutch Patent Application 7,102,524); modified polyisocyanates containing isocyanurate groups (of the type described, for example, in U.S. Pat. No. 3,002,973, German Patentschriften 1,022,789, 1,222,067 and 1,027,394, and German Offenlegungsschriften 1,919,034 and 2,004,048); modified polyisocyanates containing urea groups (of the type described in German Patentschrift 1,230,778); polyisocyanates containing biuret groups (of the type described, for example, in German Patentschrift 1,101,394, U.S. Pat. Nos. 3,124,605 and 3,201,372, and in British Patent 889,050); polyisocyanates obtained by telomerization reactions (of the type described, for example, in U.S. Pat. No. 3,654,106); polyisocyanates containing ester groups (of the type described, for example, in British Patents 965,474 and 1,072,956, in U.S. Pat. No. 3,567,763, and in German Patentschrift 1,231,688); reaction products of the above-mentioned isocyanates with acetals (as described in German Patentschrift 1,072,385); and polyisocyanates containing polymeric fatty acid groups (of the type described in U.S. Pat. No. 3,455,883). It is also possible to use the isocyanate-containing distillation residues accumulating in the production of isocyanates on a commercial scale, optionally in solution in one or more of the polyisocyanates mentioned above. It is also possible to use mixtures of the polyisocyanates described above.
In general, it is preferred to use readily available polyisocyanates, such as 2,4- and 2,6-toluene diisocyanates and their isomer mixtures (xe2x80x9cTDIxe2x80x9d); diphenyl methane diisocyanate (xe2x80x9cMDIxe2x80x9d); polymethylene poly(phenylisocyanates) of the type obtained by condensing aniline with formaldehyde, followed by phosgenation (xe2x80x9ccrude MDIxe2x80x9d); and polyisocyanates containing carbodiimide groups, urethane groups, allophanate groups, isocyanurate groups, urea groups, or biuret groups (xe2x80x9cmodified polyisocyanatesxe2x80x9d). The commercially available phosgenation products of aniline/formaldehyde condensates are the most preferred isocyanates to be used in the present invention.
The isocyanate-reactive component used to produce the polyurethane composition includes either (1) a combination or blend of castor oil or a modified castor oil and a polyether polyol, or (2) a modified castor oil which is a reaction product of castor oil or a modified castor oil with a polyether polyol.
In accordance with the present invention, suitable isocyanate-reactive components include: (i) from about 20 to 90% by weight, preferably 40 to 80% by weight, based on total weight of the isocyanate-reactive component, of castor oil having an OH number of from 160 to 170, a viscosity of from 500 to 900 mPaxc2x7s at 25xc2x0 C., and a water content of less than 0.5% by weight, based on the total weight of castor oil, and (ii) from about 10 to 80% by weight, preferably 20 to 60% by weight, based on total weight of isocyanate-reactive component, of a polyether polyol having an OH number of from 28 to 700, preferably from 112 to 500, a functionality of from 3 to 8, preferably from 4 to 7, most preferably 2 to 3, a number average molecular weight of from about 240 to about 6,000, preferably from about 400 to about 4,000, most preferably from about 400 to about 2,000, and a viscosity of from 50 to 35,000 mPaxc2x7s, preferably from 500 to 25,000 mPaxc2x7s, at 25xc2x0 C. It has been found that polyether polyols prepared from alkylene oxides in which at least 70% by weight, preferably at least 90% by weight, of the alkylene oxide content is propylene oxide are particularly suitable for the present invention. It is also advantageous to use an isocyanate-reactive component containing less than 0.5% by weight, preferably less than 0.1% by weight, based on total weight of isocyanate-reactive component of water.
Suitable polyether polyols useful in component b) include polyethers prepared, for example, by the polymerization of epoxides such as ethylene oxide, propylene oxide, butylene oxide, tetrahydrofuran, styrene oxide, or epichlorohydrin, optionally in the presence of Lewis acids such as BF3, or prepared by chemical addition of such epoxides, optionally added as mixtures or in sequence, to starting components containing reactive hydrogen atoms, such as water, alcohols, or amines. Examples of starting components include: ethylene glycol, 1,3- or 1,2-propanediol, 1,2-, 1,3-, or 1,4-butanediol, trimethylolpropane, 4,4xe2x80x2-dihydroxydiphenylpropane, aniline, ammonia, ethanolamine, and ethylene diamine. Sucrose polyethers of the type described, for example, in German Offenlegungsschriften 1,176,358 and 1,064,938 may also be used. Polyethers which contain predominantly primary hydroxyl groups (up to about 90% by weight, based on all of the hydroxyl groups in the polyether) are also suitable. Polyethers modified by vinyl polymers of the kind obtained, for example, by the polymerization of styrene and acrylonitrile in the presence of polyethers (e.g., U.S. Pat. Nos. 3,383,351, 3,304,273, 3,523,093, and 3,110,695 and German Patent 1,152,536) are also suitable, as are polybutadienes containing hydroxyl groups. Particularly preferred polyether polyols include polyoxyalkylene polyether polyols, such as polyoxypropylene diol, polyoxybutylene diol, and polytetramethylene diol, as well as polyoxypropylene polyoxyethylene triols.
Other suitable polyether polyols include the so-called xe2x80x9cPHD polyolsxe2x80x9d, which are prepared by reaction of an organic polyisocyanate, hydrazine, and a polyether polyol. U.S. Pat. No. 3,325,421 discloses a method for producing suitable PHD polyols by reacting a stoichiometric or substoichiometric quantity (relative to diamine) of polyisocyanate dissolved in a polyol having a molecular weight of at least 500 and a hydroxyl number of no more than 225. See also U.S. Pat. Nos. 4,042,537 and 4,089,835.
Other polyether polyols useful in the present invention include the so-called xe2x80x9cpolymer polyolsxe2x80x9d, which are prepared by polymerizing styrene and acrylonitrile in the presence of a polyether. See, for example, U.S. Pat. Nos. 3,383,351, 3,304,273, 3,523,093, 3,652,639, 3,823,201 and 4,390,645.
The most preferred polyethers are polyoxypropylene polyethers that do not contain ethylene oxide.
Any of the known low molecular weight organic diols or triols may optionally be included in the isocyanate-reactive component b) of the present invention in an amount of up to 10% by weight, based on total weight of component b). Suitable organic diols and triols have equivalent weights of from about 31 to 99. Examples of such diols and triols include: 2-methyl-1,3-propranediol; ethylene glycol; 1,2- and 1,3-propanediol; 1,3-, 1,4- and 2,3-butanediol; 1,6-hexanediol; 1,10-decanediol; diethylene glycol; triethylene glycol; tetraethylene glycol; dipropylene glycol; tripropylene glycol; glycerol; trimethylolpropane; neopentyl glycol; cyclohexanedimethanol; and 2,3,4-trimethylpentane-1,3-diol. Preferred diols and triols include dipropylene glycol and tripropylene glycol.
The reaction mixture from which the polyurethanes used in the present invention are produced also contains a catalyst c) for catalyzing the reaction between isocyanate groups and hydroxyl groups (i.e., a urethane catalyst). Such catalysts are well known in the art and are generally used in an amount which is no greater than 0.5 parts by weight per 100 parts by weight of isocyanate-reactive component, preferably from 0.0001 to 5 parts by weight, most preferably from 0.0001 to 0.1 parts by weight. Suitable catalysts include the organometallic catalysts. Preferred catalysts c) are organic tin compounds. The organic tin compounds are preferably tin (II) salts of a carboxylic acid such as tin (II) acetate, tin (II) octoate, tin (II) ethyl hexoate and tin (II) laurate and tin (IV) compounds such as dibutyl tin oxide, dibutyl tin dichloride, dibutyl tin diacetate, dibutyl tin dilaurate, dibutyl tin maleate, dioctyl tin diacetate and the like. Of course, it is also possible to use any of the urethane catalysts which are well known to those skilled in the art of polyurethane chemistry. It is preferred to use organometallic compounds.
The catalyst can be added separately to the polyurethane-forming reaction mixture or it may be combined with the isocyanate-reactive component prior to combining the polyisocyanate and polyol components.
Catalysts which catalyze the reaction of isocyanate groups with water (e.g., tertiary amines) should not be included in the polyurethane-forming reaction mixture.
Optionally, fillers can be used in the present invention. The fillers useful herein are also known. Useful fillers include calcium carbonate, barium sulfate, kieselguhr, whiting, mica, glass fibers, liquid crystal fibers, glass flakes, glass balls, aramide fibers, and carbon fibers. In addition, ground solid plastics (such as polyurethane scrap), rubber wastes (such as from tires), or any kind of ground rubber may be used.
If fillers are used, they can be added to either the polyisocyanate or the isocyanate-reactive component prior to forming the polyurethane-forming reaction mixture or they may be separately metered into the mixture.
In the practice of the invention, preferably liquid polyisocyanate component a) is mixed with isocyanate reactive component b) in the presence of a urethane catalyst c) at an NCO:OH equivalent ratio of from 1.4:1 to 0.9:1, preferably from 1.1:1.0 to 1.0 to 1.0.
The polyurethane geotextile composites having improved water resistance of the present invention can be formed as a liner for a ditch and/or canal.
In one embodiment of the present invention, the ditch and/or canal lining is made with a machine such as that described in U.S. Pat. No. 5,639,331 (xe2x80x9cthe ""331 patentxe2x80x9d).
The ""331 patent teaches a mobile ditch lining apparatus having reservoirs for supplying raw materials such as resin, catalysts, fillers, colors or other additives. The reservoirs are connected to a mixing chamber through flexible conduit means. The delivery rate of the raw materials to the mixing chamber will vary depending upon the particular formulation and the quantity of the formulation required for a specific area of the liner being formed. The components used to produce the polyurethane composition having improved water resistance are mixed in the mixing chamber.
From the mixing chamber, the polyurethane composition having improved water resistance is applied to one or more geotextiles. The geotextiles are pulled from a vat containing the polyurethane composition having improved water resistance through an adjustable die. The opening of the die evenly distributes of the polyurethane on the geotextile(s), determines how much polyurethane is dispensed on the geotextile(s), and also controls the thickness of the polyurethane-impregnated geotextile composite. The polyurethane-impregnated geotextile is then cut to the desired length and placed in the canal or ditch where it conforms to the surface and cures to form a polyurethane geotextile composite liner. Installing the polyurethane-impregnated geotextile liners in such a way that they overlap to a certain extent assures that a seamless permanent flexible polyurethane composite liner is obtained after curing of the polyurethane.
In another embodiment of the present invention, the polyurethane composition having improved water resistance is applied to the geotextile by spraying using commercially available two-component polyurethane spray equipment. The polyurethane-impregnated geotextile is subsequently placed in the ditch or canal where it conforms to the surface and cures to form a polyurethane geotextile composite. The geotextile can also first be cut to size, placed in the canal or ditch and subsequently sprayed with the polyurethane composition having improved water resistance. Preferably, the geotextile with the still liquid polyurethane on it is rolled with a paint roller to allow the polyurethane to penetrate through the geotextile and onto the surface of the ditch or canal.
It is also feasible to first spray the polyurethane onto one geotextile and then apply another geotextile over the first polyurethane impregnated geotextile.
In another embodiment of the invention, the polyurethane composition having improved water resistance is first sprayed on any cracked or broken concrete of a concrete lined ditch or canal and subsequently a geotextile is placed over the polyurethane-coated concrete in a manner such that the geotextile absorbs the still liquid polyurethane to form a polyurethane-impregnated composite which subsequently cures to form a solid yet flexible polyurethane geotextile composite.
State of the art sprayable polyurethane formulations are not useful in the present invention because they exhibit gel times of only several seconds. In order to prepare polyurethane geotextile composites at the site of a ditch or canal to be lined in accordance with the present invention using a polyurethane composition having improved water resistance, a gel time of at least five minutes, preferably more than 10 minutes is required.
If additional layers of polyurethane geotextile composite are desirable, any of the above processes can be repeated one or more times.
The thickness of the polyurethane geotextile composite can be varied over a wide range but usually measures from about 50 microns to about 500 microns.
The amount of polyurethane applied to the geotextile(s) can be varied but usually the amount of polyurethane applied per square meter of geotextile ranges from 1 kg to 20 kg, preferably from 2 kg to 5 kg.
If desirable several layers of the polyurethane-impregnated geotextile(s) may be applied over each other to obtain a composite of higher strength and dimensional stability. Such multi-layered composite(s) are actually preferred for lining an earthen canal or ditch.